Catalysts for converting gas to liquids

Travis Williams thinks we’ll be using liquids to fuel our cars for a long time to come. While electric vehicles will have their uses, he expects energy in the liquid form to remain the fuel of choice. As oil becomes more challenging to find and extract, supplies of gas seem to be almost endless. So an ideal situation would be to have a way of converting gas to liquid. This requires catalysis. Travis Williams and his colleagues are developing new organometalic catalysts which will hopefully make this process a reality.

Transcript

Robyn Williams: We now turn to energy options and a way we shall be driving in the future. Travis Williams is a professor of chemistry at the University of Southern California and he's looking at gaseous ways to move forward. How's it going?

Travis Williams: Dynamically. Any given time or place in the world, the price of feedstocks, the availability of natural resources is going to change. There are places on the surface of the Earth where the price of natural gas is less than zero, and in those places, man, that would be a great feedstock if we had, for example, a simple chemical technology to take the gas methane CH4 to a liquid methanol, CH3OH, then we could decompose that over a fuel cell and power an electrical device, or methanol to olefin conversion we can get into gasoline. And the mantra of our discipline in organometallics is 'have the catalytic conversion technologies when and where we need them'. And like the chameleons that came before us, we're going to have to be energy and feedstock chameleons, and the role of my discipline I think is to make sure that we have the catalytic technologies we need when and where we need them.

Robyn Williams: Yes, the catalysts are very flexible, they're abundant, and there's a tremendous centre at the University of Sydney where Thomas Maschmeyer is talking about any number of ways of bringing the technology forward. Which ones are you working on particularly?

Travis Williams: Right now we've enjoyed some pretty good success in devising molecular catalysts for the de-hydrogenation of ammonia borane. Ammonia borane, NH3BH3, is a simple inorganic small molecule. It is the most hydrogen dense at 20 weight percent of small molecules of its kind, metal hydrides and the like. It's an air stable crystalline solid, it's a solid, it's not a gas, so that's nice. It's not a liquid, which is a little less nice. I don't think it is really reasonable to think of NH3BH3 as the ultimate carrier for cars, although my neighbours down at Intelligent Energy in Long Beach point to the fact that there are hydrogen powered taxicabs on the streets of London which are powered by this small molecule. But if you think about weight efficiency, it is an incredibly weight efficient medium.

For example, one of our larger scale reactions…and I say that tongue in cheek...we did a reaction with maybe 100mg of this ammonia borane, loaded it up with 40mg of catalyst and 200mg of solvent. And you can dehydrogenate that, and if you were to take the hydrogen 170ml that you would generate from that reaction and then oxidise it over a fuel cell, it would give 15mAhours of stored energy for half a gram of materials. By contrast, your car battery, lead acid battery, is 15amphours on 5.2kilograms. That's 10 times the weight energy density in the stored hydrogen as in the lead acid battery. And I like to think about how much gasoline we are spending moving lead acid batteries around this country.

Robyn Williams: Yes, just moving weight around which you don't need to.

Travis Williams: And so I like to think about this ammonia borane in very weight sensitive applications. For example, I'm a bicycle commuter in the Hollywood Hills and unfortunately Rampart, and there are some mornings where it is nice and chilly where I could use hydrogen driven bicycles. And if you think about how many bicycle commuters, maybe not in this country but around the world, that could make use of such a technology, if we could get the weight right and the storage right and if we can get the catalysis right, there may be a market.

Robyn Williams: Of course people are saying that the crust of the Earth is actually packed full of natural gas. When will your system be developed to do the kind of work that you hope for?

Travis Williams: The problem with natural gas is the same problem with hydrogen; it's a gas and you've got to compress it. You've got to do something so that the vehicle doesn't explode, so that the vehicle has a reasonable fuel capacity. Our best hydrogen car, the BMW, is a $250,000 automobile with a 240-mile fuel capacity. Not even the American consumer would buy into that. Natural gas, is wonderful an energy feedstock as that is, we've got to get a way to get it into liquids, to be able to use it broadly in transportation fuel.

However, in that C1 story as you go up the oxidative spectrum from natural gas, the next one is methanol which could be the carrier. It's a liquid, it is very energy dense, a nice feedstock. The next one up is carbon monoxide. That's the feedstock that the Germans were using to make gasoline Fischer-Tropsch style, and there are places in the world where it's economical still to use that technology. If you keep going you get to formic acid, and then ultimately to CO2.

The chemical problem is how do you go from CO2 back down that ladder into things we can get into gasoline? And now I would say instead of trying to take ammonia borane and get it into bigger consumer products, we're starting to ask the question now at the other end of the ladder; how can we use our catalytic technology to look at CO2 and knock it down into feedstocks that we might get into vehicles, that might actually be a drop in replacement for liquid gasoline.

Robyn Williams: Imagine using carbon dioxide as a chemical basis for a fuel. It turns the problem right round, doesn't it. Professor Travis Williams at the University of Southern California.